ALBERT

Description: Author(s): X. Montiel, T. Kloss, C. Pépin, S. Benhabib, Y. Gallais, and A. Sacuto We discuss the possible existence of a spin singlet excitation with charge ± 2 ( η mode) originating the A 1 g Raman resonance in cuprate superconductors. This η mode relates the d -wave superconducting singlet pairing channel to a d -wave charge channel. We show that the η boson forms a particle-particle… [Phys. Rev. B 93, 024515] Published Wed Jan 20, 2016

Description: 〈span〉〈div〉SUMMARY〈/div〉We present a new model of time-dependent flow at low latitudes in the Earth’s core between 2000 and 2018 derived from magnetic field measurements made on board the 〈span〉Swarm〈/span〉 and CHAMP satellites and at ground magnetic observatories. The model, called 〈span〉CoreFlo-LL.1〈/span〉, consists of a steady background flow without imposed symmetry plus a time-dependent flow that is dominated by geostrophic and quasi-geostrophic components but also allows weak departures from equatorial symmetry. Core flow mode amplitudes are determined at 4-month intervals by a robust least-squares fit to ground and satellite secular variation data. The 〈span〉l〈/span〉〈sub〉1〈/sub〉 norm of the square root of geostrophic and inertial mode enstrophies, and the 〈span〉l〈/span〉〈sub〉2〈/sub〉 norm of the flow acceleration, are minimized during the inversion procedure. We find that the equatorial region beneath the core–mantle boundary is a place of vigorous, localized, fluid motions; time-dependent flow focused at low latitudes close to the core surface is able to reproduce rapid field variations observed at non-polar latitudes at and above Earth’s surface. Magnetic field acceleration pulses are produced by alternating bursts of non-zonal azimuthal flow acceleration in this region. Such bursts are prominent in the longitudinal sectors from 80–130°E and 60–100°W throughout the period studied, but are also evident under the equatorial Pacific from 130°E to 150°W after 2012. We find a distinctive interannual alternation in the sign of the non-zonal azimuthal flow acceleration at some locations involving a rapid crossover between flow acceleration convergence and divergence. Such acceleration sign changes can occur within a year or less and, when the structures involved are of large spatial extent, they can give rise to geomagnetic jerks at the Earth’s surface. For example, in 2014, we find a change in the sign of the non-zonal azimuthal flow acceleration under the equatorial Pacific as a region of flow acceleration divergence near 130°E changes to a region of flow acceleration convergence. This occurs at a maximum in the amplitude of the time-varying azimuthal flow under the equatorial Pacific and corresponds to a geomagnetic jerk at the Earth’s surface.〈/span〉

Description: 〈span〉〈div〉SUMMARY〈/div〉We present a new model of time-dependent flow at low latitudes in the Earth’s core between 2000 and 2018, derived from magnetic field measurements made on board the 〈span〉Swarm〈/span〉 and CHAMP satellites and at ground magnetic observatories. The model, called 〈span〉CoreFlo-LL.1〈/span〉, consists of a steady background flow without imposed symmetry plus a time-dependent flow that is dominated by geostrophic and quasi-geostrophic components but also allows weak departures from equatorial symmetry. Core flow mode amplitudes are determined at 4-month intervals by a robust least squares fit to ground and satellite secular variation data. The 〈span〉l〈/span〉〈sub〉1〈/sub〉 norm of the square root of geostrophic and inertial mode enstrophies, and the 〈span〉l〈/span〉〈sub〉2〈/sub〉 norm of the flow acceleration, are minimised during the inversion procedure. We find that the equatorial region beneath the core-mantle boundary is a place of vigorous, localised, fluid motions; time-dependent flow focused at low latitudes close to the core surface is able to reproduce rapid field variations observed at non-polar latitudes at and above Earth’s surface. Magnetic field acceleration pulses are produced by alternating bursts of non-zonal azimuthal flow acceleration in this region. Such bursts are prominent in the longitudinal sectors from 80-130°E and 60-100°W throughout the period studied, but are also evident under the equatorial Pacific from 130°E to 150°W after 2012. We find a distinctive interannual alternation in the sign of the non-zonal azimuthal flow acceleration at some locations, involving a rapid cross-over between flow acceleration convergence and divergence. Such acceleration sign changes can occur within a year or less, and when the structures involved are of large spatial scale they can give rise to geomagnetic jerks at the Earth’s surface. For example, in 2014, we find a change in the sign of the non-zonal azimuthal flow acceleration under the equatorial Pacific, as a region of flow acceleration divergence near 130°E changes to a region of flow acceleration convergence. This occurs at a maximum in the amplitude of the time-varying azimuthal flow under the equatorial Pacific and corresponds to a geomagnetic jerk at the Earth’s surface.〈/span〉

Description: In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

Description: The climate active trace-gas carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere. A missing source in its atmospheric budget is currently suggested, resulting from an upward revision of the vegetation sink. Tropical oceanic emissions have been proposed to close the resulting gap in the atmospheric budget. We present a bottom-up approach including (i) new observations of OCS in surface waters of the tropical Atlantic, Pacific and Indian oceans and (ii) a further improved global box model to show that direct OCS emissions are unlikely to account for the missing source. The box model suggests an undersaturation of the surface water with respect to OCS integrated over the entire tropical ocean area and, further, global annual direct emissions of OCS well below that suggested by top-down estimates. In addition, we discuss the potential of indirect emission from CS2 and dimethylsulfide (DMS) to account for the gap in the atmospheric budget. This bottom-up estimate of oceanic emissions has implications for using OCS as a proxy for global terrestrial CO2 uptake, which is currently impeded by the inadequate quantification of atmospheric OCS sources and sinks.

Description: In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

Description: Changes in the global ocean circulation produce, via motional induction, time-varying geomagnetic signals. On long length and time scales these signals are hidden beneath larger core-generated signals but, due to their location at Earth’s surface, on sufficiently short length scales and considering month to interannual timescales they may be detectable in measurements made by low-Earth-orbit magnetic survey satellites such as the Swarm mission. Such signals would provide a new source of information related to ocean circulation and conductivity variations. Here, we investigate this question using forward simulations of the magnetic signals generated by (i) the oceans, using the ECCO v4r4 ocean circulation model and a realistic electrical conductivity model for the Earth (Velimsky et al., 2021), and (ii) the core dynamo, using an advanced numerical geodynamo model (Aubert et al., 2017) that in its latest version correctly simulates the relevant timescales of core processes (waves, advection etc.). We use these to generate synthetic satellite observations based on real orbits from the Swarm mission, and simulated orbits of the proposed NanoMagSat mission. We find it is possible to recover ocean-generated secular variation (SV) and secular acceleration (SA) signals from 6 months of low-earth-orbit satellite data in these synthetic tests. It is expected that there will be significant benefits from using data from the NanoMagSat mission when considering shorter periods and an ionospheric field is present; further work is needed in this direction.